With the widespread use of two-way radio communication, it has become necessary to provide transceivers with the capability for transmitting and receiving in a number of frequency bands in order to effectively communicate in a plurality of nets or in an area where radio traffic is heavy. Also, it is desirable to be able to switch from channel to channel rapidly and accurately without the necessity for employing difficult or unwieldly tuning procedures.
One approach has been to provide a multi-channel transceiver with multiple position selector switches which automatically set the transmitter and/or receiver sections to the proper frequency. It is common practice in transceivers of this type to employ the selector switches to place a crystal of particular frequency characteristics in the circuit of the crystal controlled oscillators associated with the receiver mixer and the transmitter modulator.
To facilitate communication between two transceivers, some of the prior art devices associate a certain transmit frequency with a certain receiver frequency so that the transmit frequency of the second unit is the receive frequency of the first unit, and the receiver frequency of the second unit is the transmit frequency of the first. Other devices, however, require that the transmit and receive channels be selected independently.
There are inherent difficulties with both of the last mentioned channel selector arrangements. In the first instance, since there are only as many frequency combinations available as there are transmit or receive channels, the capacity of the transceiver is substantially limited. In the second instance, the user must always correlate the transmit and receive frequencies for the particular station he is communicating with to assure two-way operation. One arrangement suffers from inflexibility and the other from lack of ease in channel selection.